For the treatment of middle ear disorders such as exudative otitis media and blue drum (middle ear cholesterin granuloma), treatment instruments called "tympanostomy tubes" are inserted through the tympanic membrane by myringotomy, retained for an appropriate period of time to drain the exudates from the middle ear cavity to the outside through the tubes, and drawn out after the functional recovery of the middle ear.
The tympanostomy tubes therefore necessitate the easy insertion through an incision in the tympanic membrane, the efficient drainage of the exudates (viscous fluids), and no extrusion (no falling) from the tympanic membrane for a short period of time. Further, the tubes are required to be excellent in affinity for organisms, and to cause no allergy. The tubes also necessitate the easy infusion of steroid fluids and the easy removal of residual fluids when the steroid fluids are infused therethrough. Furthermore, it is also required that the inside of the middle ear cavity can be easily observed through the tubes in the treatment.
Various kinds of tubes have been proposed as the tympanostomy tubes. For example, a tube 4 shown in FIG. 1(A) is called a grommet type tube, and made of a polyethylene resin (coated with a silicone compound). This tube is expanded in the trumpet form by the viscous exudates as indicated by the arrows after its insertion. A tube 4 shown in FIG. 1(B) is formed of a Teflon resin as an integral body in the hourglass form. A tube 4 shown in FIG. 1(C) is similarly formed of a Teflon resin as an integral body in such a form that it can be easily retained in parallel with the external auditory meatus. A tube 4 shown in FIG. 1(D) is called a wide-collar type tube, and made of a silicone compound. An internal flange 8 is enlarged to enable long-term retention, and notches 9 are formed for easy insertion. A tube 4 shown in FIG. 1(E) is a T type tube, and made of a silicone compound. An inner flange 10 can be folded when inserted, and unfolded in the T form after insertion. A tube 4 shown in FIG. 1(F) is called a Castelli vent type tube, and made of a silicone compound. This tube is provided with internal and external flanges 11. A tube 4 shown in FIG. 1(G) is a parallel type tube, and made of a silicone compound. This tube has a structure similar to that of the tube 4 shown in FIG. 1(F). However, notches 12 are formed in the internal flange.
Further, tympanostomy tubes (permanent ventilation tubes of the middle ear) are also described in U.S. Pat. Nos. 3,982,545 and 5,047,053.
Furthermore, tympanostomy tubes made of titanium are described in S. D. Handler et al., International Journal of Pediatric Otorhinolaryngology, 16, 55-60 (1988).
Such a tympanostomy tube is inserted through the tympanic membrane, for example, as shown in FIGS. 2(A) and 2(B). The tympanic membrane 1 is incised, for example, laterally, as shown in FIG. 2(B), and a tube 4 is retained in the incision 2 thus formed by use of a tube insertion instrument 3 such as a forceps as shown in FIG. 2(A). In FIG. 2(A), reference numeral 5 designates the external ear cavity (external auditory meatus), reference numeral 6 designates the tympanic cavity, reference numeral 7 designates the middle ear cavity, and reference numeral 10 designates the exudate accumulated in the middle ear cavity.
Although various kinds of tympanostomy tubes are thus proposed, the grommet type tube shown in FIG. 1(A) has the advantage of easy insertion, but the disadvantage of easy extrusion. The tube 4 shown in FIG. 1(E) has the advantage of difficult extrusion due to the flange unfolded in the T form, but the disadvantage of inferior drainage caused by the T-shaped structure. The conventional tympanostomy tubes further include the following general common disadvantages.
That is, as shown in FIG. 1(H), any one of these tubes has a lumen 13 having the same diameter throughout the length thereof. FIG. 1(H) indicates a cross sectional view of the tube 4 shown in FIG. 1(B) as a typical example. As a result, these tubes have the disadvantage that the inside of the middle ear cavity is difficult to be observed after insertion thereof in the treatment.
In this case, the lumens 13 may be increased in diameter to make it easy to observe the inside of the middle ear cavity. However, these tubes are generally made of plastics or rubbers, so that an increase in diameter of the lumens 13 necessarily causes a thin wall thickness, resulting in decreased strength and easy deformation. The diameter of the lumens must therefore be necessarily decreased, which makes it difficult to observe the inside of the middle ear cavity. A smaller diameter is liable to result in inferior drainage of the exudates. A problem is therefore encountered in the infusion of steroid fluids and the removal of residual fluids when the steroid fluids are infused through the tubes.
Further, plastics and rubbers have the disadvantage of being poor in affinity for organisms. It is also considered that the tubes are formed of metals such as gold (Au) alloys. However, the gold alloys are heavy, having a high specific gravity, and have problems with regard to processability and cost.
The conventional tympanostomy tubes therefore have merits and demerits, and can not be fully satisfied.